The present invention relates to printing devices, and, in particular, to a method and apparatus for predicting the end of life of a printhead.
Inkjet printing mechanisms may be used in a variety of different printing devices, such as plotters, facsimile machines and inkjet printers, collectively referred to herein as printers. These printing mechanisms typically use a printhead to shoot drops of ink onto a page or sheet of print media. Some inkjet print mechanisms utilize a type of printhead called a cartridge that carries a self contained ink supply back and forth across the media. In the case of a multi-color cartridge, several printheads and reservoirs may be combined into a single unit, which may also be referred to as a printhead.
Other inkjet print mechanisms, known as xe2x80x9coff-axisxe2x80x9d systems, propel only a small amount of ink in the printhead across the media, and include a main ink supply in a separate reservoir, which is located xe2x80x9coff-axisxe2x80x9d from the path of printhead travel. Typically, a flexible conduit or tubing is used to convey the ink from the reservoir to the printhead. A printhead may also have a cap or capping mechanism such that when the printhead is not printing, the printhead is covered. This may serve to prevent the printhead from drying and/or to otherwise protect the printhead from the environment.
Each printhead includes very small nozzles through which the ink drops are fired. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett Packard Company. In a thermal ejection system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
To print an image, the printhead is scanned back and forth across above the media in an area known as a print zone, with the printhead shooting drops of ink as it moves. By selectively energizing the resistors as the printhead moves across the media, the ink is expelled in a pattern on the media to form a desired image (e.g., picture, chart or text). The nozzles are typically arranged in one or more linear arrays. If more than one linear array is utilized, the linear arrays may be located side-by-side on the printhead, parallel to one another, and substantially perpendicular to the scanning direction. As such, the length of the nozzle arrays defines a print swath or band. That is, if all the nozzles of one array were continually fired as the printhead made one complete traverse through the print zone, a band or swath of ink would appear on the sheet. The height of this band is known as the xe2x80x9cswath heightxe2x80x9d of the printhead, the maximum pattern of ink which can be laid down in a single pass.
The orifice plate of the printhead tends to accumulate contaminants, such as paper dust, and the like, during the printing process. Such contaminants may adhere to the orifice plate for various reasons including the presence of ink on the printhead, or because of electrostatic charges that may build up during operation. In addition, excess dried ink may accumulate around the printhead. The accumulation of ink or other contaminants may impair the quality of the output by interfering with the proper application of ink to the printing medium. Also, if color printheads are used, each printhead may have different nozzles which each expel different colors. If ink accumulates on the orifice plate, a mixing of different colored inks, known as cross-contamination, can result during use. If colors are mixed on the orifice plate, the quality of the resulting printed product can be affected. Furthermore, the nozzles of an ink-jet printer can clog, particularly if the printheads are left uncapped for a period of time. For these reasons, it is desirable to service the printhead by clearing the printhead orifice plate of such contaminants and ink on a routine basis to prevent the build up thereof. This may be accomplished by a service procedure where a printhead expels ink, is brought in contact with a wiper and expels ink again, also called a spit, wipe spit procedure. In some printers this service procedure is performed at the end of a print job based on certain criteria, for example, the number of drops fired since the last spit, wipe, spit procedure, the time a printhead has been uncapped, upon a user request, when power has first been applied to the printer, etc. Service procedures such as the spit, wipe, spit procedure are desirable to maintain print quality but also contribute to increased throughput time because of the time required to perform the procedure. These types of procedures also contribute to a shorter printhead life because the wiping action may degrade the nozzle plate over time by scratching and distorting its surface.
U.S. Pat. No. 5,455,608 describes how a printer may schedule service on a printhead based on the result of a drop detection step. Before starting a plot the printer performs a drop detection on all printheads present to detect if any nozzles are non-firing, also referred to as a xe2x80x9cnozzle outxe2x80x9d condition. If a nozzle out condition is detected in a printhead, the printer triggers an automatic recovery servicing process for servicing the malfunctioning printhead to clear or otherwise recover the malfunctioning nozzle.
This process includes a sequence of nozzle recovery or clearing procedures of increasing severity. At the end of each procedure a new drop detection test is performed on the printhead, to detect if the printhead is fully recovered. If the drop detection test indicates that a nozzle out condition continues to exist, another servicing procedure is performed. If, after a predetermined number of procedures, the printhead is still not fully recovered (i.e. at least one nozzle is still out) the user is instructed to replace the printhead or to discontinue the current nozzle check. Thus, a xe2x80x9cnozzle healthxe2x80x9d detection is performed before each print job and recovery procedures are performed based on a fixed threshold, in this example, at least one nozzle remaining non-firing.
If the printer is not able to fully recover the failing nozzles or if some nozzles are intermittent, the system may attempt to use error hiding techniques to compensate for these failures. However, there is a maximum number of failing nozzles for which the system will not be able to compensate. If the system is unable to compensate for the failing or intermittent nozzles, the system may run the recovery servicing process at the beginning of each print job, whenever the nozzle health indicates that a servicing process is required, or in response to a user request. This may continue until the printhead has been fully recovered or replaced. This may lead to an unacceptable loss of throughput and a loss of printer productivity because the automatic recovery process is very time consuming, and consumes a large quantity of ink, particularly if a priming function is included in the recovery process. In some instances, before each plot the printer may direct the user to replace the printhead or to discontinue the current nozzle check.
It is possible for a nozzle to fail during printing. If this happens, the maximum number of nozzles out, for which the system is unable to compensate, may be exceeded. This could result in less than desirable overall image quality. The probability of a nozzle failing during a print job is made more likely by certain trends. There is a trend toward wider printing areas, and thus wider plotters, to accommodate wider media. At the present time plotters accommodating sixty inch wide media are commonly available. In addition to larger printing widths, the length of print jobs continues to increase. The number of ink compositions available for use is also proliferating in order to provide the number of colors and quality desired by users. Correspondingly, the number of printheads present in a plotter to deliver these inks is also increasing. As the number of printheads increases, the number of ink reservoirs is also increasing, with a trend toward having one reservoir per printhead for increased ink capacity. An additional trend is an increase in job density, that is, the complexity of plots requested by users.
It would be advantageous to alert a user about the probability of finishing a print job within a given set of quality criteria, preferably before the print job begins. It would also be advantageous to alert a user before starting a job in the event that there is a low probability of meeting the minimum quality requirements for a print job, allowing the user either to ignore the alert, or to take action to correct the problem. In this way, time, media, ink, etc. are less likely to be wasted.
The invention provides for a method and apparatus for printing a print job including determining which nozzles of a printhead are currently failing, estimating a number of additional printhead nozzles that will fail while printing the print job, calculating a maximum number of failing nozzles that may not be exceeded in order to maintain a specified quality level for the print job, and determining if the number of currently failing printhead nozzles added to the estimated number of additional printhead nozzles that will fail exceeds the calculated maximum number of failing nozzles. The invention also includes providing a notification in the event that the number of currently failing printhead nozzles added to the estimated number of additional printhead nozzles that will fail exceeds the calculated maximum number of failing nozzles.